You'd give them an extra skill increase not only over Gray Elves, but over everyone else as well. Aielyn's calculation crucially misses that a lot of the grey elven stat advantage is in the very useless Appearance stat. Granted, Charisma isn't much better, so the "actual" difference is -1. If you play a fighting class, Mana doesn't matter, and it's +1.
Giving High Elves Archery with no downside will simply result in people using High Elves over Gray Elves for everything ever. Wizards like slaying ammo, too, after all, and with HP casting nerfed they have more use for missiles than before. High elven wizards are already barely weaker than gray elven wizards; it's because they are so similar that they're already used in the manner in which this RFE intends them to be used.
I've played tons of high elven fighter types; they have their own style compared to the "strong" fighting races such as orcs, dwarves, drakelings or trolls. I can't agree with the "middle child syndrome" image that Grey forms at all. If anything, I honestly think I've played more high elves than gray elves overall, and certainly a much greater variety of classes with a high elf rather than a gray elf, because there are only like five dedicated spellcasting classes, and for everything else high elf is the better elf. If anything, the "middle child syndrome" would be induced by the addition of mist elves (only it turns out gray elves are safe because mist elves are currently only really good at dying).
I want to stress that there's probably a good reason, from a lore perspective, that High Elves and Gray Elves share so many similarities. If there are to be significant differences between the two in talents or culture, it's up to Thomas to tell us what they are. Anything we're going to come up with is basically arbitrary at this point. After all, Gray Elves and High Elves both get Sun's Messenger and are divided by one point of Dx - on what basis do we presume that High Elves are significantly more talented at using bows?